Enantiopure [Cs+/Xe⊂​Cryptophane]⊂​FeII 4L4 Hierarchical Superstructures

Hierarchically nested hosts offer new opportunities to control the guest binding of the inner host, functionalize the cavity of the outer host, and investigate communication between different layers. Here we report a self-assembled triaza­truxene-based FeII 4L4 capsule, which was able to encapsulate a covalent cage, crypto­phane-111 (CRY). The resulting cage-in-cage complex was capable of accommodating a cesium cation or xenon atom with altered guest binding behavior compared to the CRY alone. A crystal structure of the Russian doll complex [Cs+⊂​CRY]⊂​FeII 4L4 unambiguously demonstrated the unusual encapsulation of a cation within a capsule bearing a 8+ charge. Moreover, the binding of enantio­pure CRY occurred with high enantio­selectivity (530-fold) between the two enantiomers of the tetrahedron. This discrimination resulted in stereo­chemical information transfer from the inner covalent cage to the outer self-assembled capsule, leading to the formation of enantio­pure [guest⊂​cage]⊂​cage complexes. The stereo­chemistry of the tetrahedron persisted even after displacement of CRY with an achiral guest.